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| Book/Report | FZJ-2020-00788 |
2001
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/24154
Report No.: juel-3868
Abstract: Magnetoencephalography is a non-invasive technique to study electrophysiological processesin the living human brain. These relatively new technique offers a very high temporal resolution,where the measured signals are rather independent of the differences of conductivitywithin the human head. Modern whole head systems allow the simultaneous measurement ofthe magnetic flux at more than hundred locations outside the head.However, the source localisation accuracy of the such systems highly depend on the accuracyof the measurement procedure and the quality of the data. The thesis presented here addressesquestions relating to the localisation capability of magnetoencephalography (MEG), with emphasiseon testing the accuracy of a typical whole head MEG system before any source reconstructionis applied.In particular, we have investigated the reproducibility of the head coordinate system includingvariability for different operators in order to estimate errors introduced by the head framedefinition. We further investigated the head localisation procedure and provide some estimatesabout head movements during a typical MEG investigation. Thereby, we have developedstrategies to improve both the variability of the head frame definition and the head locationaccuracy. We will show that the use of a thermoplastic mask effectively reduces the interoperatorvariability and provides a head based coordinate system that is robust across differentoperators. We have also introduced changes in the head location procedure where the improvementshave reduced the head location error by a factor of more than 2 during real measurements.At the end of the thesis we addresse the question of "how well can MEG localise neuromagneticsources" by applying the well known equivalent current dipole (ECD) approach onphantom data, where we have tried to simulate MEG measurements (with known sources)under realistic conditions.
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